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Georgia Institute of Technology (Center for Organic Photonics and Electronics (COPE)) and Purdue University researchers have developed efficient solar cells using natural substrates derived from plants such as trees. Just as importantly, by fabricating them on cellulose nanocrystal (CNC) substrates, the solar cells can be quickly recycled in water at the end of their lifecycle. To date, organic solar cells have been typically fabricated on glass or plastic. The CNC substrates on which the solar cells are fabricated are optically transparent, enabling light to pass through them before being absorbed by a very thin layer of an organic semiconductor. The substrates have a low surface roughness of only about two nanometers. During the recycling process, the solar cells are simply immersed in water at room temperature. Within only minutes, the CNC substrate dissolves and the solar cell can be separated easily into its major components.

The researchers report that the organic solar cells reach a power conversion efficiency of 2.7 percent, an unprecedented figure for cells on substrates derived from renewable raw materials, but this parameter falls far below the 10-percent threshold met by rival fabrication methods (i.e., petroleum and glass). So, there's still significant work to be done before the team can improve production and achieve parity with those less "recyclable" options. The group plans to achieve this by optimizing the optical properties of the solar cell's electrode

This research was funded by the U.S. Department of Energy (Office of Science, Office of Basic Energy Sciences), by the Air Force Office of Scientific Research, by the Office of Naval Research, and the U.S. Department of Agriculture-Forest Service.